In a bidirectional remote control system, a remote controller is operated to apply a command by an infrared ray to a variety of controlled units. When the controlled units receive the command, each unit generates a response signal by an infrared ray as confirmation which is applied to the remote controller. If response signals are applied to the controller at the same time, response signals collide and interfere with each other, causing difficulty in the bidirectional communication.
In other to prevent the signals from colliding, in the bidirectional remote control system, a collision detecting measure, so called CSMA/CD (carrier sense media across/collision detect), is performed.
FIG. 6 shows a waveform of the response signal in the form of pulses intermittently generated from one of the controlled units. In the CSMA/CD system, the unit is temporarily shifted to a signal receiving state during a signal stop period R so as to detect if a response preparing signal from the other controlled unit or the remote controller is received. If the signal is received, the unit stops to generate the response signal for a predetermined time.
However, the response preparing signal may not be received from the other controlled unit because of the disposition of the unit. If the generated response preparing signal is not received, it is impossible to effectively use the CSMA/CD system. Furthermore, construction of circuits for the CSMA/CD system is complicated to increase manufacturing cost.